Method for flip chip bonding by utilizing an interposer with embedded bumps

ABSTRACT

The present invention relates to a method for flip chip bonding by utilizing an interposer with embedded bumps. The method comprises (a) providing a first element having a first surface; (b) forming an interposer onto the first surface; (c) forming a plurality of openings on the interposer; (d) forming a plurality of bumps in the openings, wherein the height of the bumps is smaller than the depth of the openings; (e) providing a second element having a plurality of pre-solders; and (f) bonding the first surface onto the second element, so that the pre-solders are disposed in the openings and in contact with the bumps. As a result, the self-alignment between the pre-solders and the bumps can avoid the shift between the first element and the second element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for flip chip bonding, andmore particularly, to a method for flip chip bonding by utilizing aninterposer with embedded bumps.

2. Description of the Related Art

FIG. 1 shows a conventional method for flip chip bonding by utilizing anunderfill tape with embedded bumps. The conventional method is describedas follows. First, a chip 10 having a chip surface 11 is provided. Then,an underfill tape 12 is adhered to the chip surface 11. Then, aplurality of openings 13 are formed on the underfill tape 12 by laserdrilling. Then, a plurality of bumps 14 are formed in the opening 13 byplating, wherein the composition of the bumps 14 is 63% by weight of tinand 37% by weight of lead, and the height of the bump 14 is equal to thedepth of the opening 13 so that the bump 14 can fill the opening 13precisely.

Then, a substrate 15 having a substrate surface 16 is provided, whereinthe substrate surface 16 has a plurality of pre-solders 17 correspondingto the openings 13. The chip 10 is pressed to the substrate 15 byutilizing a bond head 18, wherein the chip surface 11 faces thesubstrate surface 16 so that the pre-solders 17 are in contact with thebumps 14. Finally, a reflow step with high temperature (for example,above 200° C.) and high pressure (for example, about 30 Kgm) is appliedto the chip 10 and the substrate 15 to fuse the pre-solders 17 and thebumps 14 so as to form a flip chip bonding.

The shortcoming of the conventional method is poor alignment precision.Because the bumps 14 fill the openings 13 precisely, the bottom surface19 of the underfill tape 12, which is in contact with the pre-solders17, is a flat surface. Therefore, during the pressing procedure, asliding movement between the chip 10 and the substrate 15 will cause ashift therebetween, which makes the product defective.

Consequently, there is an existing need for a novel and improved methodfor flip chip bonding to solve the above-mentioned problem.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a method for flipchip bonding by applying an interposer (such as underfill tape orB-stage material) with embedded bumps to a chip, wherein the bumps donot fill the openings of the interposer completely so as to form aplurality of recessions. When the chip is pressed to a substrate, thepre-solders of the substrate can fill the recessions. As a result, theself-alignment between the bumps and pre-solders in the openings canavoid the sliding movement between the chip and the substrate.

Another objective of the present invention is to provide a method forflip chip bonding by utilizing an interposer with embedded bumps,comprising:

(a) providing a first element having a first surface;

(b) forming a interposer onto the first surface;

(c) forming a plurality of openings on the interposer;

(d) forming a plurality of bumps in the openings, wherein the height ofthe bumps is smaller than the depth of the openings;

(e) providing a second element having a plurality of pre-solders; and

(f) bonding the first element and the second element, so that thepre-solders is disposed in the openings and in contact with the bumps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional method for flip chip bonding by utilizing anunderfill tape with embedded bumps; and

FIGS. 2 to 6 show a method for flip chip bonding by utilizing aninterposer with embedded bumps according to the preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 to 6 show a method for flip chip bonding by utilizing aninterposer with embedded bumps according to the preferred embodiment ofthe present invention. The method is described as follows. First, afirst element, such as a chip 20, is provided. The chip 20 has a firstsurface 21. Then, an interposer, such as an underfill tape 22, isadhered to the first surface 21. Then, a plurality of openings 23 areformed on the underfill tape 22 so as to expose the pads (not shown) ofthe chip 20. The openings 23 may be formed by any conventional method,such as laser drilling, and exposing and developing.

Then, referring to FIG. 4, a plurality of bumps 24 are formed in theopening 23 by plating. The composition of the bumps 24 is 63% by weightof tin and 37% by weight of lead, or 5% by weight of tin and 95% byweight of lead. Alternatively, the bumps 24 may be gold bumps or copperbumps. The height of the bumps 24 is smaller than the depth of theopenings 23 so as to form a plurality of recessions 231. That is, thebumps 24 do not fill the openings 23 completely.

Then, referring to FIG. 5, a second element, such as a substrate 25, isprovided. The substrate 25 has a second surface 26 on which a pluralityof pre-solders 27 are disposed. The position of the pre-solders 27corresponds to that of the openings 23. The height of the pre-solders 27is equal to or larger than the depth of the recessions 231 (thedifference between the depth of the openings 23 and the height of thebumps 24) so that the pre-solders 27 can fill the recessions 231completely.

The chip 20 is bonded to the substrate 25 by utilizing a bond head 28,wherein the first surface 21 faces the second surface 26 so that thepre-solders 27 are accommodated in the openings 23 and are in contactwith the bumps 24. In the embodiment, the chip 20 is pressed onto thesubstrate 25. Alternatively, the substrate 25 is pressed onto the chip20.

Finally, a reflow step with high temperature (for example, above 200°C.) and high pressure (for example, about 30 Kgm) is applied to the chip20 and the substrate 25 for about twenty minutes so that the underfilltape 22 can fill the gap between the chip 20 and the substrate 25, andthe pre-solders 27 and the bumps 24 are fused to form a flip chipbonding, as shown in FIG. 6.

In the embodiment, the first element is a chip and the second element isa substrate. However, it is understood that the first element may be asubstrate, the second element is a chip, and the underfill tape isadhered to the substrate. Additionally, in another embodiment, the firstelement is a substrate, the second element is a wafer, and the underfilltape is adhered to the substrate. A plurality of pre-solders are formedon the wafer that is then sliced into a plurality of dice. Finally, thedice are mounted onto the substrate.

In the embodiment, the interposer is an underfill tape. However, it isunderstood that the interposer may be a B-stage material, which is asemi-solid adhesive. The B-stage material is coated on the first surfaceof the first element, then is heated to become semi-solid, and then toproceed the above-mentioned process of forming openings, plating bumps,pressing and reflow. It should be noted that during the reflow process,the B-stage material will become a plastic adhesive and fill the gapbetween the first element and the second element. Therefore, the B-stagematerial needs to be maintained at a certain temperature (for example175° C.) for a certain length of time (for example thirty minutes) tobecome fully hardened.

According to the present invention, the self-alignment between the bumps24 and the pre-solders 27 in the openings 23 can avoid the slidingmovement between the first element and the second element.

While several embodiments of the present invention have been illustratedand described, various modifications and improvements can be made bythose skilled in the art. The embodiments of the present invention aretherefore described in an illustrative but not restrictive sense. It isintended that the present invention may not be limited to the particularforms as illustrated, and that all modifications which maintain thespirit and scope of the present invention are within the scope asdefined in the appended claims.

1. A method for flip chip bonding by utilizing an interposer withembedded bumps, comprising: (a) providing a first element having a firstsurface; (b) forming an interposer onto the first surface; (c) forming aplurality of openings having depths on the interposer; (d) forming aplurality of bumps in the openings, wherein the heights of the bumps isare smaller than the depths of the openings; (e) providing a secondelement having a plurality of pre-solders; and (f) bonding the firstelement and the second element, so that the pre-solders are disposed inthe openings and in contact with the bumps, wherein the heights of thepre-solders are equal to or larger than the difference between thedepths of the openings and the heights of the bumps.
 2. The methodaccording to claim 1, wherein the first element is a chip and the secondelement is a substrate.
 3. The method according to claim 1, wherein thefirst element is a substrate and the second element is a chip.
 4. Themethod according to claim 1, wherein the first element is a substrateand the second element is a wafer, the method further comprises a stepof cutting the wafer to form a plurality of dice after step (e), and thestep (f) is mounting the dice onto the substrate.
 5. The methodaccording to claim 1, wherein the step (f) is pressing the first elementonto the second element.
 6. The method according to claim 1, wherein thestep (f) is pressing the second element onto the first element.
 7. Themethod according to claim 1, wherein the interposer is an underfilltape.
 8. The method according to claim 1, wherein the interposer is aB-stage material. 9.-10. (canceled)
 11. The method according to claim 1,wherein the interposer of the step (b) is adhered to the first surface.12. The method according to claim 1, wherein the interposer of the step(b) is coated to the first surface.
 13. The method according to claim 1,wherein the openings of the step (c) are formed by laser drilling. 14.The method according to claim 1, wherein the openings of the step (c)are formed by exposing and developing.
 15. The method according to claim1, further comprising a reflow step after the step (f) so as to fuse thepre-solders and the bumps.
 16. The method according to claim 1, whereinthe composition of the bumps is 63% by weight of tin and 37% by weightof lead.
 17. The method according to claim 1, wherein the composition ofthe bumps is 5% by weight of tin and 95% by weight of lead.
 18. Themethod according to claim 1, wherein the bumps are gold bumps.